Knowledge of an aircraft's trajectory, whether that be planned or already executed, is useful for a number of reasons. Moreover, it is often useful to be able to share knowledge of an aircraft's trajectory, although there is sometimes a need for knowledge of that trajectory to remain confidential between trusted parties.
By trajectory, an unambiguous four-dimensional description of the aircraft's path is meant. The trajectory description may be the evolution of the aircraft's state with time, where the state may include the position of the aircraft (e.g. the position of the aircraft's centre of mass) and, optionally, the evolution of other aspects of its motion such as velocity, attitude and weight. Thus, the trajectory may be represented as an indication of each of these typical aircraft states at consecutive points in time during the flight.
Methods exist that allow aircraft trajectories to be calculated from aircraft intent. Aircraft intent is a description of how the aircraft is to be flown, for example expressed as instructions using a formal language. The description provides a complete description of the aircraft's behaviour such that all degrees of freedom of motion are defined and such that a unique trajectory may be calculated unambiguously from the description. The trajectory may be calculated using a trajectory computation infrastructure that, in addition to the aircraft intent data, uses a description of the aircraft performance and a description of the atmospheric conditions as further inputs. Co-pending U.S. patent application Ser. No. 12/679,275 published as US 2010-0305781 A1, also in the name of The Boeing Company, describes aircraft intent and trajectory computation in more detail, and the disclosure of this application is incorporated herein in its entirety by reference.
Aircraft intent allows an aircraft's trajectory to be predicted unambiguously by solving a set of differential equations that model both aircraft behaviour and atmospheric conditions. The aircraft intent may be derived from flight intent, as follows. Flight intent may be thought of as a generalisation of the concept of a flight plan, and so will reflect operational constraints and objectives such as intended or required route and operator preferences. Generally, flight intent will not unambiguously define an aircraft's trajectory, as the information it contains need not close all degrees of freedom of the aircraft's motion. Put another way, there are likely to be many aircraft trajectories that would satisfy a given flight intent. Thus, flight intent may be regarded as a basic blueprint for a flight, but that lacks the specific details required to compute unambiguously a trajectory.
For example, the instructions to be followed during a standard terminal arrival route (STAR) or a standard instrument departure (SID) would correspond to an example of flight intent. In addition, airline preferences may also form an example of flight intent. To determine aircraft intent, instances of flight intent like a SID procedure, the airline's operational preferences and the actual pilot's decision making process are combined. This is because the aircraft intent comprises a structured set of instructions that are used by a trajectory computation infrastructure to provide an unambiguous trajectory. The instructions should include configuration details of the aircraft (e.g. landing gear deployment), and procedures to be followed during manoeuvres and normal flight (e.g. track a certain turn radius or hold a given airspeed). These instructions capture the basic commands and guidance modes at the disposal of the pilot and the aircraft's flight management system to direct the operation of the aircraft. Thus, aircraft intent may be thought of as an abstraction of the way in which an aircraft is commanded to behave by the pilot and/or flight management system.
Aircraft intent is expressed using a set of parameters presented so as to allow equations of motion to be solved. These parameters may be ground-referenced or air-referenced parameters or a combination of both. The theory of formal languages may be used to implement this formulation: an aircraft intent description language provides the set of instructions and the rules that govern the allowable combinations that express the aircraft intent, and so allow a prediction of the aircraft trajectory.
Aircraft intent is especially useful in planning flights and missions of aircraft. Expressing aircraft intent using formal languages provides a common platform for the exchange of flight information and allows different interested parties to perform trajectory calculations. Thus, this method lends itself to collaborations where two or more parties require access to a planned trajectory. However, there are situations where details of a planned trajectory should remain confidential. In this sense, aircraft intent can be disadvantageous as, if aircraft intent data were to be intercepted by an undesirable third party, that party could determine unambiguously the planned trajectory from the intercepted aircraft intent data.
Thus there is a need for the secure transmission of a description of an aircraft trajectory. In particular, methods that make use of existing infrastructure would be particularly beneficial.